1. Field of the Invention
The present invention relates generally to the field of digital electronics, and more particularly to an apparatus and method for detecting the video mode of a video signal from a graphics card.
2. Description of the Related Art
Various conventional electronic units, such as video displays or computer display units, receive and process video signals for eventual display. In a computer unit, a graphics card is typically used to generate analog video data for display on a cathode ray tube (CRT) display unit.
However, in recent years flat panel display units have been introduced in the marketplace and have gained popularity due to the many advantages of those units. For example, flat panel display units consume less power than conventional CRT display units. Flat panel display units are also relatively smaller in size and lighter in weight than CRT display units. Also, as flat panel technology improves, flat panel display units will more likely become less expensive than CRT display units. Additionally, LCD-based flat panel display units, in particular, expose users to less radiation emission than conventional CRT display units. Furthermore, unlike CRT display units, flat panel display units have no "flicker" which often causes eyestrain and headaches for many users. Moreover, unlike CRT display units that suffer from some bending and distortions near the edges of the viewable area of the CRT screen, flat panel images remain solid at the corners. The above-mentioned advantages (as well as the increasing popularity of flat panel based computer units) serve as incentives for designers to seek solutions that permit flat panel display units to replace CRT display units in desktop computer systems.
However, there are problems in integrating a computer unit with a flat panel display unit. Currently, notebook vendors use specifically designed graphic cards that output necessary control signals for driving LCD flat panel display units. In contrast, the graphic cards in conventional computer systems are not designed to generate the necessary control signals for driving LCD flat panel display units.
A video mode is defined by the timing parameters of the video signal. The timing parameters include the resolution value, the vertical timing parameters and the horizontal timing parameters, as described hereinbelow.
If a flat panel display unit is used in place of a CRT display unit in a computer system, the video mode of the video data from the computer unit must be determined so that processing circuitry can drive the flat panel display unit in order to display the video data. However, a graphics card can generate different modes. In addition, for video signals with the same resolution, different graphics cards may generate different timing parameters. Additionally, the video data from the computer graphics card must be converted into a format that is suitable for display in a flat panel unit. Thus, to integrate a flat panel display unit with a computer unit and expect both to function properly or optimally, it is necessary to detect the video mode correctly.
A prior attempt for automatically detecting the video mode of a video signal is disclosed in commonly-assigned U.S. patent application Ser. No. 08/876,846 to Biao Zhang and Jemm Yue Liang, filed Jun. 16, 1997 and entitled AUTOMATIC CLOCK RECOVERY SYSTEM FOR DISPLAY APPLICATIONS. Zhang discloses a method of detecting the video mode of a video signal based on the total number of horizontal synchronous (Hsync) pulses within one video frame. The total number of Hsync pulses within one frame of the video signal is defined as "total lines". U.S. patent application Ser. No. 08/876,846 is fully incorporated herein by reference.
However, Zhang's approach is unable to differentiate two different video modes that both have the same number of total lines per video frame. Zhang's approach is also unable to differentiate a first video mode from a second video mode wherein the first video mode has a larger number of total lines than the second video mode and wherein the first video mode has less "active lines" per video frame than the second video mode. An active line is one that contains video information and can be displayed on a screen and seen by an end-user.
Therefore, there is a need for an apparatus and method that will automatically and accurately detect the different video modes. There is also a need for an apparatus and method for differentiating two different video modes with the same number or a substantially close number of total lines per video frame. There is also a need for an apparatus and method for differentiating between at least two modes wherein the first mode has more total lines per video frame than the second mode, but has less active lines per video frame than the second mode. There is also a need for an apparatus and method that permit a computer with a typical graphics card to function with flat panel display units.